Kevin is 50 years old and William is 12 years old. How many years will it take until Kevin is only 3 times as old as William?
Explanation: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Kevin will be $50 + y$ years old and William will be $12 + y$ years old. At that time, Kevin will be 3 times as old as William. Writing this information as an equation, we get: $50 + y = 3 (12 + y)$ Simplifying the right side of this equation, we get: $50 + y = 36 + 3 y$ Solving for $y$ , we get: $2 y = 14$ $y = 7$.